Radiation therapy has been employed to treat tumorous tissue. In radiation therapy, a high energy beam is applied from an external source towards the patient. The external source produces a collimated beam of radiation that is directed into the patient to the target site. The dose and placement of the dose must be accurately controlled to ensure that the tumor receives sufficient radiation, and that damage to the surrounding healthy tissue is minimized.
Existing radiotherapy systems use x-ray as the radiation beam. In such systems, the ability to control the dose placement is limited by the physics of the beam, which necessarily irradiates healthy tissue on the near-side and far-side of a target region as it passes through the patient. Thus, it may be desirable to use protons as the source of the radiation. By controlling the energy of the protons, the protons will stop at a precise location within the patient. In this way, tissue on the far-side of the target region does not receive any radiation dose. Further, because the dose provided by a proton is concentrated at a “Bragg peak” around the area where the proton stops, the dose to healthy tissue on the near-side of the target region may also be reduced.
Sometimes, it may be desirable to selectively modulate an energy of the proton beam such that the Bragg peak can hit target regions that are located at different depths in the patient. Also, if proton technique is to be used to implement arc therapy, in which the beam source is rotated about the target region, it may also be desirable to selectively modulate the energy of the proton beam dynamically during the treatment procedure. This is especially the case if the target region is closer to one side of the patient than others. In this case, the proton beam may need to penetrate less tissue to reach the target region at certain gantry angle, and more tissue at other gantry angles. However, existing proton systems do not allow an energy of the beam to be modulated accurately, reliably, and effectively during a treatment procedure.